Heart failure is a major cause of death and disability. Some common forms of heart failure include idiopathic dilated cardiomyopathy (etiology unknown), hypertensive cardiomyopathy (similar to idiopathic dilated but with antecedent hypertension), hypertrophic cardiomyopathy, and ischemic cardiomyopathy. Regardless of the initial cause, studies suggest that the enhanced chronic sympathetic drive, which is a consequence of the depressed cardiac output, ultimately plays a role in the development of clinically significant cardiac dysfunction and the progression of heart failure. Thus, it would be advantageous to develop methods to assess cardiovascular diseases in an individual.